1. Field of the Invention
The invention generally relates to wood composites and coatings. More specifically, the invention relates to a method of selectively coating, wood composites, and to the coated composites.
2. Description of Related Technology
Wood composites, a type of molded composite article, include man-made boards of bonded wood sheets and/or lignocellulosic materials, commonly referred to in the art by the following, exemplary terms: fiberboards such as hardboard, medium density fiberboard, and softboard; chipboards such as particleboard, waferboard; and strandboard. Wood composites also include man-made boards comprising combinations of these materials.
These wood composites can be used as columns, floors, floor underlayment, roof sheathings, ceilings, walls, wall coverings, wainscots, partition systems, doors, and stairs in the construction of homes, offices, and other types of buildings, as well as furniture components, such as chairs, tables, countertops, cabinets, and cabinet doors, and other uses, such as bulletin boards, for example.
Many different methods of manufacturing these wood composites are known in the art such as, for example, those described in Hsu et al. U.S. Pat. No. 4,514,532 and Newman et al. U.S. Pat. No. 4,828,643, the disclosures of which are hereby incorporated herein by reference. The principal processes for the manufacture of fiberboard include: (a) wet felted/wet pressed or “wet” processes; (b) dry felted/dry pressed or “dry” processes; and, (c) wet felted/dry pressed or “wet-dry” processes. Synthetic resins, such as urea-formaldehyde resins, melamine resins, phenol-formaldehyde resins, or modified phenol-formaldehyde resins, are often used as binders in these processes.
Wood composites made by these or other known methods appear noticeably different from natural woods. For example, wood composites do not possess the color, grain, or texture changes characteristic of natural woods. To make wood composites appear similar to natural wood, the composites typically are finished by multiple applications of coatings, stains, or glazes, which give the composites a more natural wood-like appearance. Alternatively, wood composites are, wet finished overlaid or using either vinyl films, printed papers, or hot transfer foil materials that have been imprinted with designs simulating a natural-appearing woodgrain pattern.
Several methods for finishing wood composites by application of stains or glazes are known to those skilled in the art. For example, Pittman et al. U.S. Pat. No. 5,534,352 discloses a method of finishing wood composite panels that includes the steps of providing a textured substrate, applying a ground coat to the substrate, and applying a buffing glaze to the substrate. Thereafter, the buffing glaze is selectively removed from the substrate, a sealer is applied to retain the remaining buffing glaze in textured ticks of the substrate, and gravure prints and a protective topcoat are applied to the substrate. These methods, through selective removal of the buffing glaze, allow the substrate to mimic the gradual shadings present in natural wood. However, the printing cylinders used to provide the woodgrain prints are expensive and have a limited useful life. Furthermore, these methods do not provide for the use of different patterns on the same board; each board is printed using a given set of print cylinders.
Lightweight vinyl films or heat transfer foils are commercially available, and may be used to impart a natural wood-like appearance to wood composites. Heat transfer foils are typically backed by a carrier film for ease of handling and application. These vinyl films and heat transfer foils typically are applied to the composite by heat and/or pressure using either a membrane press or a vacuum press. For example, “Formella, Membrane Pressing: No Longer a Mystery,” Furniture Design & Manufacturing (March 1996), discloses a method of using a membrane press to apply a heat transfer foil to wood composites to provide a natural wood-like appearance. However, the method requires separate rolls of film for each design format or change in size of a given wood composite design in order for the heat transfer foil to remain in-register with the molded wood composite.
Heretofore it has been impractical to precisely register the film to a molded wood composite in either a membrane press or vacuum press in a one-step operation because the film is likely to wrinkle, shrink, and/or move, resulting in a part which is out of register. Furthermore, commercially-available vinyl film materials may not consistently draw into deep molded (e.g., greater than nine millimeters (mm)) profiles. Use of vinyl films does not allow the artisan to imprint color or grain changes in register onto the wood composite without dedicated rolls for each size and product pattern. Such color or grain changes may be accomplished through the use of pre-printed films designed especially for the application, however, these films are extremely costly, difficult to register, and may draw unevenly, stretching or breaking when drawn or molded in multiple directions.
In view of the foregoing, it would be desirable to provide a wood composite coating method that allows for color and/or grain changes in register, as well as enhancing the embossing of wood composite appearance in a single step, while maintaining both a consistently high yield of finished wood composite board and the appearance of natural wood.